A 3rd Generation Partnership Project (3GPP) Long Term Evolution Advanced (LTE-A) Rel-10/11/12 is an advance on a Long Term Evolution (LTE) Rel-8/9 release, and an LTE-A system has a bandwidth requirement higher than a bandwidth requirement of an LTE system, and supports a peak data rate up to 1 G/s downlink and 500 M/s uplink. To meet a requirement of LTE-A, in the LTE-A system, a carrier aggregation (CA) technology is used as a method for expanding system bandwidth of the LTE-A system, and a multiple-antenna enhancement technology (multiple-input multiple-output MIMO) and a coordinated multipoint technology (CoMP) are used to improve a data rate and system performance.
In the LTE-A, various technologies are used to improve the data rate. However, with rapid development of wireless communications and generation of ultra-high rate traffic (such as a high-definition video), a wireless communications network has increasingly heavy load. How to alleviate network load becomes a hot research topic. Device-to-device (D2D) communication emerges, and becomes a major project of the LTE-A Rel-12 release. In this communications mode, user equipment (UE) may directly communicate without a need of an evolved NodeB (eNB) for forwarding; therefore, data load of the eNB is shared. In the D2D communication, a spectrum resource can be better used, spectrum utilization and a data rate are improved, and a burden on the eNB is alleviated.
In the current D2D communication, there is a contention-based distributed resource reuse method, where UE obtains a resource from a resource pool by means of contention. First, there is a predefined resource contention period, and if the UE wants to obtain a resource, the UE needs to listen for an available resource, that is, a resource in an idle state, in the resource contention period. If the UE detects the available resource by means of listening, the UE may attempt to send data in a next resource contention period on the available resource detected by means of listening. If no conflict occurs (that is, no another UE sends data on the available resource), the UE obtains the resource by means of contention; a user who obtains the resource by means of contention may send data on the resource in consecutive several resource contention periods, and in this case, another UE learns, by means of listening, that the resource is in an occupied (non-idle) state; and the resource is not released back to the resource pool until the UE stops sending data in a resource contention period.
From starting to listen for an available resource, to participating in resource contention, and then to obtaining a resource, it takes each UE a long time, which indicates a long contention-based access time; therefore, if a large quantity of UEs contends for a resource, a conflict probability is high, and UE needs to perform contention for many times to obtain an available resource, which leads to a long delay in obtaining the available resource by the UE.